This invention relates to image copying or recording devices, and more particularly, this invention relates to a system for tracking and maintaining alignment of an endless belt in an image copying or recording device.
There are presently known a variety of recording devices such as image copiers or printers utilizing an endless belt, in the form of a web or tape of latent image storing material wherein the latent image is created on the belt and "developed" by applying a toner thereto. The toner developed image is transferred to a suitable substrate such as paper and then rendered permanent by various techniques. Such devices employ electrostatic, magnetic, etc., principles.
One of the major problems experienced in operating these devices is that of tracking of the belt. Typically, the belt is supported by at least two rollers, one of which is a drive roller, which moves the belt at a constant speed in the desired direction of travel. For a variety of reasons, the belt frequently "walks" or creeps to one end or the other of the rollers thereby resulting in misalignment or even escape from the roller. Consequently, there have been many suggestions for maintaining the belt in alignment to prevent creep. Some of these prior attempts at maintaining tracking of the endless belt involve the use of crowns, grooves, helixes, or other surface distortions of one or more rollers as described in U.S. Pat. No. 3,308,929. Other proposed solutions to the problem involve the use of sensors for detecting lateral movement of the belt beyond a predetermined amount with means for tilting rollers or roller assemblies then being activated responsive to a signal from the sensor. A typical such construction is shown in U.S. Pat. No. 3,818,391. Other constructions involving edge sensing of the web and consequent movement of a carriage containing one or more rollers are shown in U.S. Pat. Nos. 3,715,027, 3,796,488 and 3,993,186.
The aforementioned prior art constructions suffer from disadvantages. They result in excessive belt wear, require frequent maintenance and adjustment or involve complex elements which are, themselves, subject to malfunction.